In recently popular electronic products such as mobile phones, personal computers and portable music players, an aluminum alloy is widely used in view of weight saving, downsizing and good workability and a plurality of screws are used to mount a component thereon.
Therefore, as an example of such a screw, Japanese Patent No. 4490358 discloses a self-tapping screw. The self-tapping screw includes a normal thread molded in a leg portion and a female screw molding thread having a larger diameter than that of the normal thread, and is configured such that the female screw molding thread is screwed to a workpiece while molding a female screw. In addition, any pitch of the normal thread is set to be the same as each other. According to the configuration, in fastening and rotating, both flank surfaces of the normal thread do not come into contact with a female thread. Thus, it is possible to reduce tightening torques and to prevent the workpiece from being cracked.